Carbon dioxide foamed fluids

Abstract

An aqueous viscoelastic surfactant (VES) fluid foamed or energized with carbon dioxide, in which the VES is more compatible with the carbon dioxide, is made by the addition of one or more than one synergistic co-surfactant. The synergist co-surfactant includes quaternary amines and ethoxylated carboxylates having a hydrophobic chain shorter than the hydrophobic chain of the VES. Improved compatibility is evidenced for a given surfactant concentration either by formation and maintenance of a foam under conditions at which the foam could not otherwise have been formed or maintained, or by either higher viscosity of the foamed fluid at a given temperature or longer foam life at a given temperature or a higher temperature at which useful fluid viscosity can be generated or maintained for a useful time. The aqueous carbon dioxide foamed fluids may be used in acidizing, acid fracturing, gravel packing, diversion, and well cleanout.

1. A fluid composition comprising a viscoelastic surfactant, carbon dioxide in a separate phase and a synergistic co-surfactant that co-operatively stabilizes the carbon dioxide-water interface, said synergistic co-surfactant being selected from a copolymer having regions of polypropylene oxide and regions of vinyl alcohol vinyl acetate, further comprising water, wherein said viscoelastic surfactant is present in a concentration of from about 0.3 to about 10%, and said synergistic co-surfactant is present in a concentration of from about 0.008 to about 4%, wherein the foam quality is from about 55% to about 80%. 
     
     
       2. The fluid composition of  claim 1  further comprising a zwitterionic surfactant having the formula:
   RCONH—(CH 2 ) a (CH 2 CH 2 O) m (CH 2 ) b —N + (CH 3 ) 2 —(CH 2 ) a′ (CH 2 CH 2 O) m′ (CH 2 ) b′ COO −   
 
       wherein R is an alkyl group that contains from about 17 to about 23 carbon atoms which may be branched or straight chained and which may be saturated or unsaturated; a, b, a′, and b′ are each from 0 to 10 and m and m′ are each from 0 to 13, provided that both m and m′ are not equal to 0; a and bare each 1 or 2 if m is not 0 and (a+b) is from 2 to 10 if m is 0; a′ and b′ are each 1 or 2 when m′ is not 0 and (a′+b′) is from 1 to 5 if m′ is 0; (m+m′) is from 1 to 14; and CH 2 CH 2 O may also be OCH 2 CH 2 . 
     
     
       3. The fluid composition of  claim 2  wherein the surfactant is a betaine. 
     
     
       4. The fluid composition of  claim 3  wherein the betaine is selected from oleylamidopropyl betaine and erucylamidopropyl betaine. 
     
     
       5. The fluid composition of  claim 1  wherein the synergistic co-surfactant improves the compatibility of the viscoelastic surfactant with the carbon dioxide. 
     
     
       6. The fluid composition of  claim 1  further comprising zirconium oxychloride. 
     
     
       7. A method of treating a subterranean formation penetrated by a wellbore comprising injecting the fluid composition of  claim 1  into said formation. 
     
     
       8. A method of treating a wellbore comprising injecting the fluid composition of  claim 1  into said wellbore. 
     
     
       9. A fluid composition comprising a viscoelastic surfactant, said viscoelastic surfactant being a zwitterionic surfactant, carbon dioxide in a separate phase and a synergistic co-surfactant that co-operatively stabilizes the carbon dioxide-water interface and wherein the ratio of surfactant to co-surfactant is from about 5:1 to about 15:1, wherein the foam quality is from about 55% to about 75% wherein said synergistic co-surfactant is selected from copolymers including regions of polypropylene oxide and regions of vinyl alcohol vinyl acetate. 
     
     
       10. A fluid composition comprising a viscoelastic surfactant, carbon dioxide in a separate phase, water and a synergistic co-surfactant selected from copolymers including polypropylene oxide regions and vinyl alcohol vinyl acetate regions, wherein said viscoelastic surfactant is present in a concentration of from about 0.3 to about 10%, and said synergistic co-surfactant is present in a concentration of from about 0.008 to about 4%, wherein the foam quality is from about 55% to about 80%. 
     
     
       11. A method of treating a wellbore comprising injecting the fluid composition of  claim 10  into said wellbore.